1. Field of the Invention
The present disclosure relates to a differential amplifier. More particularly, the present disclosure relates to a differential amplifier having improved operating characteristics.
2. Description of the Related Art
Differential amplifiers are widely used in integrated circuit (IC) devices. Differential amplifiers are designed to amplify the difference between two input signals while rejecting any common signal components. Therefore, when two signal lines are used as inputs to the differential amplifier, electrical noise commonly induced to the two signal lines will have no effect on the output signal thus allowing only the difference in signals of the signal lines to be amplified.
A conventional differential amplifier generally includes a load element, an input element and a current source. For example, a single-ended differential amplifier can be coupled to a first voltage node that is electrically coupled to an internal power supply voltage through a load element and to a second voltage node that is electrically coupled to a ground voltage through a current source, and two input elements of the single ended differential amplifier can be coupled in parallel with each other between the load element and the current source to receive an input signal and a reference voltage signal respectively.
It should be noted that as the power supply voltage used for an IC device drops, internal devices within a differential amplifier incorporated into the IC tend to inadvertently change. For example, as the internal power voltage level drops, an internal reference voltage level upon which the differential amplifier relies also drops. When this reference voltage level is low and a low level input signal is input to the differential amplifier, the response speed at which certain NMOS transistors incorporated into the differential amplifier slows and as a result the delay of the output signal increases. In other words, the level of a differential amplifier's reference voltage signal can cause an undue delay in the differential amplifier's output signal. Therefore, new technology related to differential amplifiers that are insensitive to reference voltage levels is desirable.